The invention relates to labeling machines in which labels are transferred from continuously moving backing strips via rotating applicator drums to articles such as food or medicine containers being conveyed through a labeling station. The invention is concerned in particular with preventing incorrect labels from being applied to such containers, with minimal attendant interruption of machine operation.
Packagers of foods and pharmaceuticals demand high levels of accuracy and reliability in the labelling process. Accordingly, systems have been developed for detecting the presence of incorrect labels both prior to and following label application. Generally, labeling machines that provide labeling error detection prior to the application of the labels onto the articles, are preferred to those which provide error detection following application. Labeling machines that provide labeling error detection prior to application include those disclosed in U.S. Pat. Nos. 2,551,364 (Coakley) and 4,662,971 (Adams).
The devices of Coakley halt the operation of the machine in the event that an incorrect label is detected. Although this may prevent the application of an incorrect label to an article, the attendant disruption of production adversely affects operating efficiencies.
The Adams reference discloses a device that closes a vacuum line to a rotating vacuum applicator drum in the event that an incorrect label is detected. With the vacuum line closed, the rotating drum is apparently unable to draw the label from the backing strip, and consequently the label is not applied to an article.
Interrupting the vacuum is not, however, an optimal approach for preventing the application of an incorrect label. First, vacuum interruption may not occur sufficiently quickly. Thus, unless the labels are spaced relatively far apart on the backing strip, more than a single defective label (and thus more than the one respective article) could be affected as the drum continues to rotate. Second, it may not be possible to reinstate the vacuum within the drum and resume normal operation without further attendant and disruptive delays.
There is a need therefore for labeling machines that reliably and efficiently prevent incorrect labels from being applied to articles, with minimal interruption of the labeling operation.